This invention generally relates to apparatus to conduct drilling fluids in a downhole drilling apparatus between first rotating elements and second other elements that are non-rotating or rotating at a different angular rate than the first rotating elements. One aspect of the invention concerns controlled sealing provided between juxtaposed surfaces which are relatively movable. In this regard, the relative movement is rotation about a longitudinal axis common to both sets of elements.
An example of such usage is in a steerable rotary drilling apparatus. In such an apparatus, a drill string extending from the surface of the earth to a drill bit at the bottom of a borehole is continuously rotated. Various apparatus or means for steering the direction of drilling advance may be provided near the drill bit, and generally outside the drill string. Such apparatus may provide either a sideways force on the bit or it may actually point the bit toward the desired direction. Examples of such apparatus are shown in U.S. Pat. Nos. 5,035,872, 5,113,953, 5,265,682, 5,520,255, 5,617,926 and 6,092,610. Such apparatus is generally rotationally stabilized either to a zero angular rate or an angular rate that is much less than the drill string angular rotation rate. Various means are used to provide such force or direction control. Both electrical and hydraulic means may be used. If a hydraulic means is used, it is based on pressure from the drilling fluids supplied via the interior of the drill string, and a rotary joint means is needed for conducting high-pressure drilling fluid from the interior of the rotating drill string to the direction control apparatus outside of the drill string. None of the examples of steerable rotary drilling disclosed in such referenced patents provide a suitable solution to this requirement; and none of such examples provide the unusually advantageous apparatus construction, modes of operation and results as are disclosed herein.